Method of making small metal bodies



Jan. 2, 1951 H. 1.. KREBS EI'AL 2,536,539

METHOD OF MAKING SMALL METAL BODIES Filed June 22, 1946 NNNNNNN RSfifth/(r1: Z. Kit ks BY [a S. Just/v A'T TTTT EY atented .F. 2, l95lMETHOD OF MAKING SMALL METAL BODIES Heinrich L. Krebs and Lee S. Busch,Indianapolis, Ind., assignors to P. R. Mallory & 00., Inc.,Indianapolis, Ind., a corporation of Delaware Application June 22, 1946,Serial No. 678,610

6 Claims.

of small metal bodies which utilizes a soft metal layer tosimultaneously transmit pressure onto several die recesses filled withmetal powders whereby a large number of such bodies may be pressed orcompacted in a single operation.

It is an object of the present invention to improve the method andapparatus disclosedin the said copending application.

It is another object of the invention to provide a method and apparatusfor making small compacted and sintered metal bodies of predeterminedsize and shape having substantially uniform density and structure.

The invention also contemplates a novel and improved method of makingsmall metallic parts by means of a powder metallurgical procedure whichmay be carried out on a quantity production scale at a low cost.

Other objects and advantages of the invention will be apparent from thefollowing description and accompanying drawing, in which:

Figure 1 is a vertical sectional view of a die provided with a pluralityof die cavities adapted to carry the principles of the invention intopractice;

Figure 2 is a. top plan view of the die sectionally represented inFigure 1;

Figure 3 is a vertical sectional view of the complete pressing apparatusand is illustrative of an intermediate step in the method of the presentinvention;

Figure 4 is a horizontal sectional view, having parts in elevation, ofthe apparatus, taken on line 4-4 of Figure 3;

Figure 5 is a vertical sectional view of the apparatus when carrying outthe final pressing step of the invention;

Figure 6 is a horizontal sectional view of the apparatus taken on line6-6 of Figure 5; and

Figure 7 is an enlarged sectional detail view of a single die cavity andpressure slug as they appear'after the final pressing operation.

In all the drawings the size of the die cavities has been greatlyexaggerated for reasons of clarity.

Broadly stated, in accordance with the principles of the presentinvention, there is provided a lower die member or die plate made of amaterial having substantial strength and wear resistance such as toolsteel. A plurality of die recesses or cavities is provided in the uppersurface of the die, the said cavities having shapes corresponding tothose of the bodies to be pressed but being slightly larger in size inorder to compensate for the shrinkage occurring during the sinteringoperation.

When carrying the method of the invention into practice the die cavitiesare coated with a suitable lubricant and are filled with the metalpowders to be compacted. The powder-filled cavities are covered byindividual tough and ductile metal slugs or pellets having diameterslarger than those of the cavities and a plane and substantiallynon-deformable pressure platen is placed over the said slugs. Uponpressure being applied to the platen, such pressure is transferred tothe individual slugs which are deformed or flattened and are caused toprotrude to some extent into the die cavities. The lower portion of eachslug will act as an independent and individual pressure plunger,automatically conforming to the surface of the die cavity and exertingpowerful compacting pressure upon the metal powder mixture therein.

The compacted metal bodies may be readily removed from the die cavitiesby moderately heating the die thereby melting the lubricant coating andcausing the bodies to drop out upon turning the die upside down.Thereafter, the compacted bodies are subjected to the usual powdermetallurgical operations such as sintering, and the like. It has beenfound that metal bodies made in accordance with the described method arecharacterized by uniform density, microstructure and physical propertiesin general and that such properties can be accurately controlled andmaintained in quantity production.

As shown in Figures 1 and 2, the apparatus of the present inventioncomprises a die plate ll formed of an annealed tool steel blank intowhich cavities I! of the desired shape are pressed by punches or othermeans. After the cavities have been formed, the die blank is heattreated to a hardness of about 60 Rockwell C and the cavities arepolished and lapped to a mirror finish. This is necessary as roughsurfaces in the cavities tend to give a rough surface to the pressedbodies and also make the removal of the said bodies after pressing morediilicult.

The finished die cavities are preferably coated with a suitable fusiblelubricant 13, for example with a 1% to 5% parafiin or stearic acidsolution in carbon tetrachloride or other volatile solvent. The die isthen tamped face down on a, paper towel or other absorbent material andwiped free of excess lubricant.

After lubrication, the die cavities are filled with the required amountof metal powder mixture M by sifting the powder through a fine sieveinto 3 the cavities with an alternate tapping and shaking motion andwiping oil? the excess powder. The resulting structure will clearlyappear from Figure 2 which is a top view of the apparatus in Figure 1showing an arrangement of die cavities coated with lubricant and filledwith metal powder.

The filled die is now readyfor pressing. As illustrated in Figure 3,over each die cavity there is placed a slug or pellet l5 of copper orany other tough and ductile metal which is readily extrudable. The slugsare preferably made of heavy copper wire, having a hardness of at least50 Rockwell B, cut into short pieces. The hardness characteristics ofthe slug are quite important because the portion of the slug which isextruded into the die cavity must conform exactly to the shape of thedie, and for best results, the surface of the slug in contact with thepowder must be flat. In addition to copper, other metals or alloys whichcan be readily extruded may be used as the pressing medium; for example,aluminum, nickel, cold rolled steel, lead or silver. The necessaryhardness, of course, depends upon the material used, but the metalshould be about three-fourths to full hard, as it is'sometimes-expressedin metallurgy.

After placing a slug in position over each of the powder filledcavities, a common pressure platen i6 is positioned over the slugs.plete assembly is then inserted into a hydraulic press and pressure isapplied ranging from about 50 to 100 tons per square inch.

As it will appear from Figures 5 and 6, during the pressing operation,the individual slugs are flattened out and their lower portions areextruded into the corresponding cavities. The extruded portions of theslugs act as individual plungers which exactly conform to the shape ofthe die cavity and cause the metal powder to be pressed to the desireddensity. This is best shown in Figure 7 which is a greatly enlarged viewof a single die cavity and cooperating slug after the pressingoperation. From this figure the plane bottom surface of the extrudedslug portion is clearly apparent.

It has been found that in order to obtain best results, it is desirableto prevent the circumferential surfaces of the slugs from touching eachother during or after the pressing operation. This will be readilyunderstood if it is considered that direct contact of adjoining slugsduring pressing would interfere with further spreading of the slugs andwith uniform extrusion of the slugs into the cavities. Direct lateralcontact of the slugs may be easily avoided by proper spatial arrangementof the die cavities and by selecting suitable initial dimensions of theslugs. For the same reasons, the preferred initial shape of the slugs iscylindrical although various other shapes such as shapes of a square orhexagonal cross section could be used with equal or similar results. Ingeneral, the slugs are used only for a single pressing operation and theflattened and extruded slugs are discarded for scrap. This, however,does not appreciably affect the cost of practicing the invention in viewof the low cost of the slugs which may be readily and inexpensively madein large quantities, for example, by chopping off short pieces from awire of the proper diameter.

After pressing, the die with the pressed pieces still in the cavities isheated to about 50 C. to 100 C. to soften the lubricant which coats thesurfaces of the cavities. The die is then inverted The comand tappedlightly against a flat surface whereupon the pressed pieces fall outreadily. The pressed compacts are then sintered by any one of severalmethods well known to those skilled in the art.

The size, shape and number of the cavities in the die will be determinedby the type of the compact or pressed body and other manufacturingconsiderations. Thus, in the case of phonograph needle points, forexample, a cone shape of the proper angle and height is required. In apractical die for making phonograph needle points the number of cavitieswas 21 and they were spaced 5%" (0.344") apart from each other. The topdiameter of the cone-shaped cavities was 0.064" and their total depthwas 0.081". The side walls of the cavities enclosed an angle of 39degrees and the bottom of the cavities was rounded out to a radius of0.005".

The composition of the metal powders is likewise subject to considerablevariations in accordancewith the specific application. A compositionwhich was found to be very satisfactory for phonograph needle tips andsimilar small articles comprised 50% osmium, 34% tungsten carbide and16% cobalt. The preferred sintering temperature for this composition wasabout 1450 C. A great variety of other metal compositions suitable forpracticing the present invention is disclosed in the copendingapplications of Franz R. Hensel and Earl I. Larsen, Serial Nos. 637,031,and 663,954. filed December 22, 1945 and April 22, 1946,respectivelyyand entitled Metal Composition for Phonograph Needles andHard Metal Compositions, respectively, both of said applications nowabandoned.

It will be noted that the present invention provides various importantadvantages. Thus, the invention provides a method and an apparatus ofgreat simplicity for making small pressed parts, such as phonographneedle tips, pen points, pivot bearings and points, cutting tools, andthe like, characterized by great uniformity of density, microstructureand other desirable physical properties.

It is also to be observed that the method of the invention employingindividual pressure slugs or pellets for each of a large plurality ofdie cavities represents a substantial advance over methods employing asingle pressure layer for all of the die cavities in requiring lowercompacting pressures and in compensating for small differences in thesize and shape of the cavities and in the quantity of metal powderintroduced into such cavities which are unavoidable in pressing metalbodies of greatly reduced dimensions.

Moreover, the invention is readily adaptable to pressing metal bodies ofminute dimensions on a quantity production scale and at a very low cost.Practicing the method involves a minimum of manual handling of theindividual bodies and yields compacts of heretofore unobtainablestructural and dimensional uniformity.

While the present invention, as to its objects and advantages, has beendescribed herein as carried out in specific embodiments thereof, it isnot desired to be limited thereby but it is intended to cover theinvention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. The method of forming powdered metal compacts which comprisesproviding a plurality of die recesses in a die plate conforming in shapeto that of the compacts to be formed, filling said recesses with metalpowder, covering each of said powder filled recesses with a ductilemetal pellet, and simultaneously applying pressure to said pellets tocause partial extrusion of said pellets into the recesses and compactingof the metal powder therein.

2. The method of forming powdered metal compacts which comprisesproviding a plurality of spaced die recesses in a plate, coating saidrecesses with a lubricant, filling said coated recesses with metalpowder, covering each of said powder filled recesses with a slug ofductile metal having a diameter larger than the surface diameter of therecesses, placing a common pressure platen over said slugs, and applyingpressure to said platen to cause progressive flattening of said slugsand their partial extrusion into the die recesses resuiting incompression and "compacting of the" metal powder therein, the spacing ofthe die recesses being so determined with respect to the final diameterof the flattened slugs that direct lateral contact of adjoining slugs iseffectively prevented during the pressing operation.

3. The method of forming small objects of powdered metals whichcomprises coating die recesses in a hard metal plate with a lubricant,filling said coated recesses with metal powder, placing a ductile copperslug having a hardness of 50 to 65 Rockwell B over each of said powderfilled recesses, covering said slugs with a common pressure platen, andapplying pressure to said platen to cause said slugs to be extruded intoand the metal powder to be compacted in said recesses.

4. The method of forming powdered metal compacts which comprisesproviding in a plate at least one dies recess conforming in shape tothat of the compacts to be formed and having a smooth inner surface,filling said recess with metal powder, covering said powder filledrecess with a ductile metal pellet, applying pressure to the top face ofsaid pellet to cause it to flow and to protrude to a limited extent intosaid recess and to accurately conform to the side walls thereof therebyto compact the metal powder in said recess, and then removing thecompact from said recess for further treatment.

5. The method of forming powdered metal compacts which comprisesproviding in a substantially non-deformable die plate a. plurality ofrecesses spacedfrom each other and having shapes conforming to those ofthe compacts to be formed, filling said recesses with metal powder,covering each of said powder filled recesses with a metal slug ofgenerally cylindrical character, simultaneously forcing a substantiallyplane pressure surface against the exposed faces of said slugs to causetheir material to fiow and to protrude to a limited extent into therespective recesses thereby to compact the powder therein, said slugshaving such ductility and hardness as to accurately conform to the wallsof the recess and to retain a substantially plane plunger-like surfacein contact with the powder, and then removing the finished compact fromsaid recesses for further treatment.

6. Apparatus for making compacts of powdered metals which comprises'ahard metal die'containing a plurality of recesses adapted to receivesaid powdered metal, a ductile copper slug positioned over each of saidrecesses, the diameter of said slugs being slightly larger than thesurface diameter of the recesses and said recesses being disposed on thehard metal body so that the copper slugs, after being enlarged bycompression against said die and said powdered metal, will not toucheach other, a common pressure platen covering said slugs, and a coatingof fusible lubricant on the walls of said recesses to facilitate removalof the pressed compacts from the recesses upon said die being heated.

HEINRICH L. KREBS. LEE S. BUSCH.

- REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,424,406 Hauptmeyer Aug. 1, 19221,545,369 Tizley July 7, 1925 1,607,389 Claus Nov. 16, 1926 2,033,735Pack Mar. 10, 1936 2,169,280 Pfanstiehl Aug. 15, 1939 2,243,809 WendelMay 27, 1941 2,267,372 Calkins et al. Dec. 23, 1941 2,298,885 Hull Oct.13, 1942 2,366,487 Burgess Jan. 2, 1945

